refs.c: add an err argument to delete_ref_loose

Add an err argument to delete_loose_ref so that we can pass a descriptive
error string back to the caller. Pass the err argument from transaction
commit to this function so that transaction users will have a nice error
string if the transaction failed due to delete_loose_ref.

Add a new function unlink_or_err that we can call from delete_ref_loose. This
function is similar to unlink_or_warn except that we can pass it an err
argument. If err is non-NULL the function will populate err instead of
printing a warning().

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
refs.c: make update_ref_write update a strbuf on failure

Change update_ref_write to also update an error strbuf on failure.
This makes the error available to ref_transaction_commit callers if the
transaction failed due to update_ref_sha1/write_ref_sha1 failures.

Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
update-ref: use err argument to get error from ref_transaction_commit

Call ref_transaction_commit with QUIET_ON_ERR and use the strbuf that is
returned to print a log message if/after the transaction fails.

Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
refs.c: remove the onerr argument to ref_transaction_commit

Since all callers now use QUIET_ON_ERR we no longer need to provide an onerr
argument any more. Remove the onerr argument from the ref_transaction_commit
signature.

Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
refs.c: change ref_transaction_update() to do error checking and return status

Update ref_transaction_update() do some basic error checking and return
non-zero on error. Update all callers to check ref_transaction_update() for
error. There are currently no conditions in _update that will return error but
there will be in the future. Add an err argument that will be updated on
failure. In future patches we will start doing both locking and checking
for name conflicts in _update instead of _commit at which time this function
will start returning errors for these conditions.

Also check for BUGs during update and die(BUG:...) if we are calling
_update with have_old but the old_sha1 pointer is NULL.

Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
refs.c: change ref_transaction_create to do error checking and return status

Do basic error checking in ref_transaction_create() and make it return
non-zero on error. Update all callers to check the result of
ref_transaction_create(). There are currently no conditions in _create that
will return error but there will be in the future. Add an err argument that
will be updated on failure.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
refs.c: update ref_transaction_delete to check for error and return status

Change ref_transaction_delete() to do basic error checking and return
non-zero of error. Update all callers to check the return for
ref_transaction_delete(). There are currently no conditions in _delete that
will return error but there will be in the future. Add an err argument that
will be updated on failure.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
refs.c: make ref_transaction_begin take an err argument

Add an err argument to _begin so that on non-fatal failures in future ref
backends we can report a nice error back to the caller.
While _begin can currently never fail for other reasons than OOM, in which
case we die() anyway, we may add other types of backends in the future.
For example, a hypothetical MySQL backend could fail in _being with
"Can not connect to MySQL server. No route to host".

Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
refs.c: add transaction.status and track OPEN/CLOSED/ERROR

Track the status of a transaction in a new status field. Check the field for
sanity, i.e. that status must be OPEN when _commit/_create/_delete or
_update is called or else die(BUG:...)

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
tag.c: use ref transactions when doing updates

Change tag.c to use ref transactions for all ref updates.

Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
replace.c: use the ref transaction functions for updates

Update replace.c to use ref transactions for updates.

Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
commit.c: use ref transactions for updates

Change commit.c to use ref transactions for all ref updates.
Make sure we pass a NULL pointer to ref_transaction_update if have_old
is false.

Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
sequencer.c: use ref transactions for all ref updates

Change to use ref transactions for all updates to refs.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
fast-import.c: change update_branch to use ref transactions

Change update_branch() to use ref transactions for updates.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
branch.c: use ref transaction for all ref updates

Change create_branch to use a ref transaction when creating the new branch.

This also fixes a race condition in the old code where two concurrent
create_branch could race since the lock_any_ref_for_update/write_ref_sha1
did not protect against the ref already existing. I.e. one thread could end up
overwriting a branch even if the forcing flag is false.

Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
refs.c: change update_ref to use a transaction

Change the update_ref helper function to use a ref transaction internally.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
receive-pack.c: use a reference transaction for updating the refs

Wrap all the ref updates inside a transaction.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
fast-import.c: use a ref transaction when dumping tags

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
walker.c: use ref transaction for ref updates

Switch to using ref transactions in walker_fetch(). As part of the refactoring
to use ref transactions we also fix a potential memory leak where in the
original code if write_ref_sha1() would fail we would end up returning from
the function without free()ing the msg string.

This changes the locking slightly for walker_fetch. Previously the code would
lock all refs before writing them but now we do not lock the refs until the
commit stage. There is thus a very short window where changes could be done
locally during the fetch which would be overwritten when the fetch completes
and commits its transaction. But this window should be reasonably short.
Even if this race does trigger, since both the old code and the new code
just overwrites the refs to the new values without checking or comparing
them with the previous value, this is not too dissimilar to a similar scenario
where you first do a ref change locally and then later do a fetch that
overwrites the local change. With this in mind I do not see the change in
locking semantics to be critical.

Note that this function is only called when fetching from a remote HTTP
repository onto the local (most of the time single-user) repository which
likely means that the type of collissions that the previous locking would
protect against and cause the fetch to fail for to be even more rare.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
refs.c: make lock_ref_sha1 static

No external callers reference lock_ref_sha1 any more so lets declare it static.

Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>